Project 4: Neural Basis of Behavioral Sequence Loops Abstract The goal of Project 4 is to understand how discrete action motifs are organized into goal-directed behavioral sequences that evolve over timescales of seconds to minutes. Behavioral sequence loops are at the highest level of our control-loop hierarchy, where they integrate high-level sensory representations and provide descending signals to guidance and motor loops. The execution of a behavioral sequence requires the ability to sustain activity (persistence), as well as the ability to switch between behaviors (fluidity). To investigate neural mechanisms of persistence and fluidity, we will study the circuits in the fly brain that control sequential behaviors such as visually guided walking, spatial navigation, and working memory. We will combine cell-type specific genetic driver lines with in vivo 2-photon imaging and electrophysiology to understand how these circuits balance competing demands to select and drive sequential behaviors. We will then use optogenetic tools to test specific circuit models of behavioral sequence generation in freely behaving flies. These studies are divided into the following three Specific Aims: Specific Aim 1: Defining the cellular basis of stochastic control of walking. Specific Aim 2: Identify the neural circuitry underlying path integration. Specific Aim 3: Investigate the network mechanisms of counter-turning behavior.